Limbic System/Hypothalamus (2) Flashcards
The function of the limbic system is what?
to reconcile higher level information (from association cerebral cortex) with more basic drives (from subcortical structures) to learn from past experiences, make immediate choices and formulate long term plans
what is the function of the limbic association cortex?
conveys highly processed sensory information which is further processed by the hippocampus (in encoding sensory impressions into long-term memory) and the amygdala (to link sensory information with emotional responses)
what is in the prefrontal cortex? Where does it project? Where does input come from?
areas of frontal lobe not contained in motor or premotor cortex; striatum; somatosensory cerebral cortex, the dorsomedial and anterior nuclei of the thalamus, and the ventral tegmental area (VTA).
What is the function of the dorsolateral frontal cortex? Damage here can cause what?
Important in attention, abstract thought and planning (executive function); reduced abilities to organize information and shift strategies in a changing environment.
What is the function of the ventraomedial frontal cortex and orbitofrontal cortex? Damage here can cause what?
inhibition of inappropriate behavior; disinhibition - impulsiveness and disregard for others
The cingulate gyrus receives input from where? Projects to where?
sensory cortex, prefrontral cortex, the thalamus (anterior nucleus and nociceptive cells); entorhinal cortex
What is the function of the cingulate gyrus? Damage here can cause what?
cingulate cortex is though to mediate the emotional correlates of pain (sadness)
anterior cingulate cortex- thought to play an esp. important role in learning (error detection and reward-based decision making); memory disorders
Hippocampal formation includes what? Receives dopaminergic input
from where?
subiculum (transition cortex, layers 3-6), dentate gyrus (archicortex, layers 1-3) and hippocampus proper (archicortex, layers 1-3); ventral tegmental area
The cingulum carries input from where to where?
cingulate gyrus to entorhinal cortex and orbitalfrontal gyri to parahippocampal gyrus
The perforant pathway conveys information from where to where?
pyramidal neurons in layer II of the
entorhinal cortex to the dentate gyrus and CA3 of the hippocampus proper
The alveal pathway conveys information from where to where?
neurons of layer III of the entorhinal cortex to
CA1 the hippocampus
The hippocampus proper can be further subdivided into what four regions?
CA1- closest to the subiculum, CA2, CA3, CA4- closest to the dentate gyrus
Cholingergic neurons in the septal nuclei project to where? The hippocampus proper projects to where via what?
hippocampal formation; septal area via precommissural fibers of the fornix
Granule cells of the dentate gyrus projects to where via what?
CA3 of the hippocampus proper via mossy
fibers
CA3 neurons of the hippocampus proper project to where via what?
CA1 neurons via Schaefer collaterals
CA1 neurons of the hippocampus proper project to where?
subiculum
The subiculum projects to where via what?
mamillary bodies via the columns of the fornix; entorhinal cortex.
What is long term potentiation?
High frequency sequence of stimulutions of the perforant pathway, massy fiber pathway or Schaffer collaterals can result in long lasting enchancement of excitatory potentials in the hippocampal neurons
LTP is thought to involve what?
an increase in calcium influx through NMDA receptors; calcium activation of calmodulin and the cognitive kinases; retrograde messenger, perhaps nitric oxide (NO) or cell adhesion proteins, acts on the presynaptic neuron
LTP and the cognitive kinases (in both the presynaptic and postsynaptic neurons) are thought to enable what?
learning and memory by enhancing synaptic transmission between neurons for relatively long periods of time
What are the cognitive kinases in LTP?
calcium/calmodulin-dependent protein kinase (CaMK), protein kinase A (PKA), protein kinase Cs (PKCs) and tyrosine kinases
What is long term depression?
Weakening of synapses due to postsynaptic receptor density, Weakening of synapses due to postsynaptic receptor density, may be involved in forgetting or negative feedback that regulates LTP.
The fornix consists of axons related to What two structures?
hippocampus proper and subiculum
Axons of the fornix initially form what? this coalesces into what?
alveus (white matter covering hippocampal formation), fimbria (where the axons collect before leaving the hippocampal formation),
Axons which originate in the hippocampus proper leave the body of the fornix at the level of what? Where do they terminate?
AC, travel dorsal to the AC, septal area as the
precommissural fornix
Axons which originate in the subiculum leave the body of the fornix at the level of what? Terminate where?
AC, travel ventral and descend in the columns of the fornix into the diencephalon to the mammillary nuclei
The mammillary nuclei project to where via what?
mammillothalamic tract (MTT) to the anterior nucleus of the thalamus
The anterior nucleus of the thalamus projects to where via what?
cingulate gyrus via the anterior limb of the
internal capsule
The amygdala receives input from where?
olfactory bulb (via lateral olfactory stria), entorhinal cortex and has reciprocal connections with the frontal and temporal neocortex
The amygdala projects to where via what path?
Ventral amygdalofugal pathway to lateral hypothalamus - direct route. Stria terminalis to ventromedial hypothalamus (VMH), septal area via the stria terminalis, dorsomedial nucleus of the thalamus which in turn projects to frontal lobe association cortex
What is the function of the amygdala?
Fear learning, involved in feeding and reproductive behavior.
Patients with damage to the amygdala have what difficulties?
cannot discriminate fearful facial
expressions from other emotional expressions. However, they can identify different people.
What is an uncinate fit?
Involvement of uncus and underlying amygdala. Strange unpleasant odor and feeling of unreality
What is Klüver-Bucy syndrome?
rarely in humans; extensive, bilateral damage to the anterior temporal lobe, esp. amygdala. Symptoms- placidity (apathy), hyperorality, hyperphagia, hypermetamorphosis (tendency to react to every visual stimulus), visual agnosia (can see but not recognize what an object is) and hypersexuality
What are causes of Klüver-Bucy syndrome?
herpes simplex encephalitis, brain surgery (usually for epilepsy), trauma, stroke and
neurodegenerative diseases
The nucleus accumbens receives input from where? What system is this?
Dopaminergic neurons in the ventral tegmental area (VTA) of the midbrain, amygdala, prefrontal cortex; mesolimbic
The nucleus accumbens projects to where? What system is this?
ventral pallidum, which projects to dorsomedial nucleus of the thalamus which projects to the prefrontal cerebral cortex; mesolimbic
What is the function of the nucleus accumbens?
Reinforcing effects of food, sex and other stimuli- mesolimbic system, Addictive drugs increase dopamine in nucleus accumbens; stimulated in an attempt to treat depression; stimulated when patients experience the placebo effect
The hypothalamus can be divided into what three major regions?
anterior, tuberal and posterior
What are the subdivisions of the anterior hypothalamus?
preoptic area (POA, not part but funct. related), Suprachiasmatic nuclei (SCN), Supraoptic nuclei (SON), Paraventricular nuclei (PVN)
POA is located where? Consists of what?
below anterior commissure and rostral to the supraoptic region of the hypothalamus; MPOA contains gonadotrophin-releasing hormone (GnRH) neurons- axonsproject to the median eminence
Suprachiasmatic nuclei (SCN) is located where? Receives input from where? Projects to where?
above the optic chiasm at the base of the 3rd ventricle, direct retinal input, area just ventral to the paraventricular nucleus
Supraoptic nuclei (SON) is located where?
caudal to the preoptic area, dorsal to the optic chiasm
SON consists of what?
magnocellular neurons containing vasopressin (anti-diuretic hormone) or oxytocin.
SON projects to where?
posterior pituitary gland and releases vasopressin and oxytocin into the general circulation
Where is the paraventricular nuclei (PVN)?
dorsal to the suprachiasmatic nuclei in close proximity to the third ventricle
What does the PVN contain?
magnocellular (ADH and oxytocin) neurons and parvocellular neurons (TRH, CRH) which project to the posterior pituitary gland or median eminence, neurons- axons project to brainstem and IML cell column of spinal cord via the medial forebrain bundle and dorsal longitudinal fasciculus.
What are the components of the tuberal hypothalamus?
VMH, arcuate nucleus,
VMH is located where? receives input from where?
dorsal to the arcuate nucleus, input from amygdala
Arcuate nucleus is located where?
close proximity to the median eminence, directly dorsal to the median eminence and pituitary gland.
Arcuate nucleus is contains what?
neurons which produce a variety of different molecules which are released into the median eminence and transported to the anterior pituitary gland; including dopamine, GHRH
Mammilary nuclei are in what portion of the hypothalamus? Receive input from where? Project to where?
posterior; hippocampal formation via the fornix, anterior nucleus of the thalamus via the mammilo-thalamic tract
What are thew 2 main fiber bundles that run through the hypothalamus?
Medial forebrain bundle and Dorsal longitudinal fasciculus
What is the Dorsal longitudinal fasciculus?
axons from neurons within the PVN project to PS CN nuclei and the IML cell collumn of spinal cord (symp); Reciprocal connection between the periaqueductal gray and tegmentum of the midbrain with medial hypothalamus; allows communication of the hypothalamus with reticular formation
What is the Medial forebrain bundle?
Diffuse group of axons found in lateral hypothalamus, Cell bodies in septal area, lateral hypothalamus, locus ceruleus and piriform cortex; terminate in: hypothalamus, midbrain tegmentum,amygdala, septal area, dorsal nucleus of vagus and raphé nuclei.
What is the role of the hypothalamus?
neuroendocrine, circadian rhythms, feeding regulation, ANS
What role does the hypothalamus play in neuroendocrine?
Small neurons produce factors (GHRH, TRH, CRH, GnRH, SS and dopamine) which are transported to the median eminence, released and carried to the ant. pit. by portal vessels; SON and PVN project to post pit (ADH, oxytocin)
What role does the hypothalamus play in circadian rhythms?
suprachiasmatic region- highly expressed gene for circadian regulation, acts as pacemaker of rhythm; pineal gland- secretes melatonin primarily at night as a result of an indirect projection
from the SCN
What role does the hypothalamus play in feeding regulation?
VMN- satiety, receptors for glucose; lateral- reg hunger; VMN- receptor for leptin (protein secreted by fat cells, may reg body weight)
What role does the hypothalamus play in ANS?
Input: Visceral info- from solitary nucleus, contains thermoreceptors and osmoreceptors; Sensory info- reticular formation (integrated, pain), Emotional- septal nuclei, amygdala and hippocampus
Output: project directly to preganglionic symp and PS neurons, or indirect projects to reticular formation
Dopamine in the ant. pituitary does what?
inhibits release of prolactin from the anterior pituitary gland.
Somatostatin does what in the ant. pituitary?
inhibits the release of growth hormone from the anterior pituitary gland and
thyroid-stimulating hormone (TSH)
Growth hormone releasing hormone (GHRH) does what?
stimulates the release of growth hormone
from the anterior pituitary gland
Corticotropin-releasing hormone (CRH) stimulates what?
release of adrenocorticotropic hormone (ACTH) from the anterior pituitary gland.
Thyrotropin-releasing hormone (TRH) stimulates what?
release of thyroid-stimulating hormone (TSH) and prolactin (PRL)
Gonadotropin releasing hormone (GnRH) stimulates what? Dysfunction of these neurons can cause what?
release of follicle stimulating hormone (FSH) and luteinizing hormone (LH):prevent the onset of puberty (Kallmann’s syndrome). After puberty onset, disrupt reproductive function
